Hatoum, Hoda

Abstract In Vitro testing is widely used to evaluate the hemodynamic performance of transcatheter aortic valves (TAVs). However, many studies assess self-expanding valves using blood analogs matched in viscosity at room temperature, despite the temperature-dependent mechanical behavior of nitinol stent frames. This study investigates the independent and combined effects of temperature and viscosity on the in vitro performance assessment of a self-expanding TAV. Rheological characterization was performed to identify water-glycerin solutions with matched viscosities at room temperature and physiological temperature (37 °C). A patient-specific aortic model was cast in silicone. A self-expanding Medtronic Evolut R valve was deployed within the compliant model and evaluated using a pulse-duplicating left heart simulator under physiological flow and pressure conditions. The transvalvular pressure gradient and effective orifice area (EOA) were calculated. Rheometry identified two fluid conditions with comparable viscosities at room and body temperatures. Heating the blood analog to 37 °C resulted in significantly reduced transvalvular pressure gradient and increased EOA compared to the viscosity-matched room temperature condition (p < 0.0001). At physiological body temperature, the higher viscosity fluid (42% glycerin) yielded further improvements in valve performance relative to the lower viscosity fluid (38% glycerin), with lower pressure drop and larger EOA (p < 0.0001). These results demonstrate that temperature-dependent effects influence the hemodynamic performance of self-expanding nitinol TAVs beyond viscosity matching alone. Combined consideration of temperature and viscosity is therefore necessary to ensure physiologically relevant in vitro assessment of self-expanding TAVs.

ABSTRACT Background This study aims to assess how Watchman FLX (Boston Scientific) and Amplatzer Amulet (Abbott) devices for left atrial appendage occlusion (LAAO) impact the flow dynamics in the LA and the risk of device‐related thrombosis (DRT). Methods Flow simulations were carried out for 12 AF patients before and after undergoing LAAO. Six patients had Watchman FLX while the other six had Amulet devices, of which three in each group had DRT. The flow parameters investigated included the LA velocities, pressure, time averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT). Low TAWSS and high OSI and RRT are generally associated with flow stasis and thrombosis. Results LA flow dynamics differed significantly between the two groups. On average, after LAAO, the Amulet patients exhibited a 25% increase in TAWSS and 24% decrease in RRT while the Watchman FLX patients exhibited, on average, a 24% decrease in TAWSS and a 23% increase in RRT. Both populations experienced an increase in LA pressure (~10% for Amulet patients and 16% for Watchman FLX patients). Increased DRT volume seems to be correlated with low TAWSS and elevated RRT. Conclusion This preliminary study suggests that the Amulet device might be associated with improved LA flow dynamics and a potentially lower incidence of DRT compared with the Watchman. However, a larger clinical study is needed to confirm these findings.

Background Stroke remains a concern after transcatheter aortic valve replacement (TAVR). Several studies attempted to identify correlates of stroke but there remains a need for better predictors. Objective This study aims to characterize the aortic arch to identify potential correlates of stroke after TAVR using a patient cohort that includes cases with and without stroke. Methods A retrospective analysis was performed on 52 patients who underwent TAVR at Mayo Clinic and Maria Cecilia Hospital. Of these patients, 26 had a stroke after TAVR and 26 did not (control). Anatomical characterization was performed on each patient. Patient-specific 3D digital models of the ascending aorta, aortic arch, and calcium were created for each patient. Geometrical measurements, including cross-sectional areas, volumes, tortuosity, curvature, and length of the model were recorded. Results There was no significant difference in the various area measurements between the two groups, but the aortic arch cross-sectional area ratio (cerebral ostia cross-sectional areas/arch cross-sectional area) was significantly higher in the stroke group. Additionally, there was no significant difference in tortuosity, curvature, aortic volume, and length of the aorta. Aortic valve calcium score, aorta calcium, and aortic arch type (I, II, or III) were not significantly different between the groups. The prevalence of a bovine arch (BA) configuration was significantly higher in the stroke group (46% vs 8% control, p < 0.05). Conclusion Aortic arch cross-sectional area ratio and BA variant were the most significant correlates of stroke after TAVR.

Abstract Background The exclusion/occlusion of the left atrial appendage (LAA) is a treatment option for atrial fibrillation (AF) patients who are at high risk of stroke and high risk of bleeding. As the role of the LAA is not well understood or explored, this study aims to assess its role on flow dynamics in the left atrium. Methods Computational fluid dynamics (CFD) simulations were carried out for nine AF patients before and after LAA exclusion. The flow parameters investigated included the LA velocities, Time Averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), Relative Residence Time (RRT), and Pressure in the LA. Results This study shows that, on average, a decrease in TAWSS (1.82 ± 1.85 Pa to 1.27 ± 0.96 Pa, p < 0.05) and a slight increase in OSI (0.16 ± 0.10 to 0.17 ± 0.10, p < 0.05), RRT (1.87 ± 1.84 Pa −1 to 2.11 ± 1.78 Pa −1 , p < 0.05), and pressure (−19.2 ± 6.8 mmHg to −15.3 ± 8.3 mmHg, p < 0.05) were observed in the LA after the exclusion of the LAA, with a decrease in low‐magnitude velocities. Conclusion The exclusion of the LAA seems to be associated with changes in LA flow dynamics. Further studies are needed to elucidate the clinical implications of these changes.

Background Acute ischemic stroke complicates 2% to 3% of transcatheter aortic valve replacements (TAVRs). This study aimed to identify the aortic anatomic correlates in patients after TAVR stroke. Methods and Results This is a single‐center, retrospective study of patients who underwent TAVR at the Mayo Clinic between 2012 and 2022. The aortic arch morphology was determined via a manual review of the pre‐TAVR computed tomography images. An “a priori” approach was used to select the covariates for the following: (1) the logistic regression model assessing the association between a bovine arch and periprocedural stroke (defined as stroke within 7 days after TAVR); and (2) the Cox proportional hazards regression model assessing the association between a bovine arch and long‐term stroke after TAVR. A total of 2775 patients were included (59.6% men; 97.8% White race; mean±SD age, 79.3±8.4 years), of whom 495 (17.8%) had a bovine arch morphology. Fifty‐seven patients (1.7%) experienced a periprocedural stroke. The incidence of acute stroke was significantly higher among patients with a bovine arch compared with those with a nonbovine arch (3.6% versus 1.7%; P =0.01). After adjustment, a bovine arch was independently associated with increased periprocedural strokes (adjusted odds ratio, 2.16 [95% CI, 1.22–3.83]). At a median follow‐up of 2.7 years, the overall incidence of post‐TAVR stroke was 6.0% and was significantly higher in patients with a bovine arch even after adjusting for potential confounders (10.5% versus 5.0%; adjusted hazard ratio, 2.11 [95% CI, 1.51–2.93]; P <0.001). Conclusions A bovine arch anatomy is associated with a significantly higher risk of periprocedural and long‐term stroke after TAVR.

Abstract Objective Our objective was to evaluate the impact of various blood pressures (BPs) on coronary perfusion and valvular hemodynamics following aortic valve replacement (AVR). Background Lower systolic and diastolic (SBP/DBP) pressures from the recommended optimal target range of SBP < 120–130 mmHg and DBP < 80 mmHg after AVR have been independently associated with increased cardiovascular and all‐cause mortality. Methods The hemodynamic assessment of a 26 mm SAPIEN 3 transcatheter aortic valve (TAV), 29 mm Evolut R TAV, and 25 mm Magna Ease surgical aortic valve (SAV) was performed in a pulsed left heart simulator with varying SBP, DBP, and heart rate (HR) conditions (60 and 120 bpm) at 5 L/min cardiac output (CO). Average coronary flow (CF), effective orifice areas (EOAs), and valvulo‐arterial impedance (Zva) were calculated. Results At HR of 60 bpm, at SBP < 120 mmHg and DBP < 60 mmHg, CF decreased below the physiological lower limit with several different valves. Zva and EOA were found to increase and decrease respectively with increasing SBP and DBP. The same results were found with an HR of 120 bpm. The trends of CF variation with BP were similar in all valves however the drop below the lower physiological CF limit was valve dependent. Conclusion In a controlled in vitro system, with different aortic valve prostheses in place, CF decreased below the physiologic minimum when SBP and DBP were in the range targeted by blood pressure guidelines. Combined with recent observations from patients treated with AVR, these findings underscore the need for additional studies to identify the optimal BP in patients treated with AVR for AS.